HEAT CONSUMPTION AND HEAT UTILIZATION. 499 



the amount so utilized will probably be covered if we estimate all the 

 water which is really chemically combined with the clay as being mechan- 

 ically held water. This course has been followed in the present esti- 

 mates. On this assumption, even a dry mix will carry about 2 per cent 

 of water, and this amount has been accordingly allowed for in the 

 previous paragraph and in Table 187. 



Heat utilized in dissociation of sulphates. A certain amount of heat 

 is taken up in dissociating any lime sulphate (gypsum) present in the 

 raw mix. Newberry has taken this as requiring 1890 B.T.U. per pound 

 of S0 3 . In marl plants the percentage of sulphates present may 

 rise to notable quantity, but in most other plants they are negligible. 

 In the present discussion the assumptions will be made that the 

 average dry mix carries 0.3 per cent of sulphur trioxide, and that 

 the usual wet mix may carry 1 per cent. The total amount of heat 

 required for the dissociation of sulphates will therefore be: 



Dry mix 600 Ibs. XO.3% X 1890 = 3,402 B.T.U. per barrel 



Wet mix " " X 1.0% X 1890 = 11,340 " 



Heat utilized in dissociation of carbonates. The most important 

 heat requirement by far is that for the dissociation of the carbonates 

 of the charge. 



The values assumed by Richards for the dissociation requirements 

 of the two carbonates are: 



Liberation of 1 kilo CO 2 from CaCO 3 =990 calories. 



" 1 " CO 2 " MgCO 3 = 407 " 



These are referred to Berthelot. They correspond respectively to 

 the two values of: 



Dissociation of 1 pound CaCO 3 requires 584 B.T.U. 

 " 1 " MgCO, " 381 " 



These values will be accepted in the following calculations for 

 the sake of uniformity, though Ostwald * quotes from Thomsen a 

 value corresponding to 765 B.T.U. for the dissociation of 1 Ib. of 

 lime carbonate. If this latter value were accepted, the quantities 

 given in the table below (188) should be reduced about 2J per cent. 

 Other values for these dissociation constants have been quoted by 

 various authorities, with a much wider range, but for the present 

 purpose those first noted will be satisfactory enough. 



Temperature required for clinkering. Widely differing statements 

 have been made as to the temperature required in order to clinker the 

 average Portland-cement mixture. 



Carpenter, in testing the Cayuga plant noted later, determined 



* Lehrbuch der allgemeinen Chemie, vol. II, pt. 1, p. 272. 



